To perform a measurement by employing a biosensor chip, a sample to be measured is introduced in the reaction portion of a biosensor, a biochemical reaction, such as an enzymatic reaction or an antigen-antibody reaction, is generated in the reaction portion, and information obtained through this biochemical reaction is output, by the biosensor chip, to a measurement apparatus that analyzes the sample. A measurement method employing a biosensor chip is performed by employing a superior molecular recognition function possessed by an organism, and has drawn attention as a method for enabling the performance of a quick and simple measurement of a chemical substance by employing only a tiny amount of a sample. As an example, the measurement method using a biosensor chip can be employed to measure the glucose content of blood (blood sugar level) or a urine sugar level, and can be used, for example, for a home health examination (self-care) for the self-control and management of diabetes.
A measurement method using a biosensor chip described in patent document 1 is known. According to this biosensor measurement method, as shown in FIG. 8, a biosensor 100 includes two leads 101 and 102, and the distal ends of the leads 101 and 102 are to be connected to two terminals 104 and 105 of a connector 103. When the biosensor 100 is connected to the connector 103, a voltage is applied using a battery 106, the resistances of electrodes are changed by a sample present in the biosensor 100, and the system function is initiated. Then, a microcomputer 107 detects, through an A/D converter 109, a change in a voltage output by a current/voltage converter 108, and starts a measurement timer. At the same time, a switch 110 is closed, and the two electrodes of the biosensor 100 are short-circuited, so that the two electrodes can be set to equal potential states, i.e., to states near a potential difference of 0 V. As a result, a potential difference that occurred between the two electrodes can be easily removed.
As another example, a measurement method employing a biosensor chip described in patent document 2 is known. According to this measurement method for employing a biosensor, as shown in FIG. 9, a biosensor 200 and a connector 201 are connected by resistors 202 and 203 arranged between the individual leads of the two electrodes and the individual terminals of the connector 201. And a GDO enzyme, a potassium ferricyanide electron acceptor, a phosphate buffer solution and a glucose substrate are introduced in the electrode system and a current flowing through the electrode system is measured. The current is detected by a detection circuit 204, and is converted into a voltage signal by a current/voltage converter 205. The thus obtained voltage signal is converted into a digital signal by an A/D converter 206, the digital signal is processed by a CPU 207 and a resultant signal is output to an LCD display device 208 and can also be recorded in a memory 209.
Patent Document 1: Japanese Patent Application Laid-Open: JP-A-8-15220
Patent Document 2: Japanese Patent Application Laid-Open: JP-A-9-274010